1. Field of the Invention
The present invention relates generally to the field of linear friction welding, and in particular, to apparatus and methods for dual axis forging for linear friction welding machines.
2. Description of the Related Art
Linear Friction Welding is a solid-state process of jointing similar or dissimilar metals that results in desirable microstructures in the weld and in the heat affected zones, producing minimal component distortion and high strength welds. In addition, linear friction welding is also a self-cleaning process, in that the oscillating motion of the process causes surface irregularities and contaminants to be expelled as flash generated during the weld, eliminating production steps.
As implied by its name, linear friction welding involves heating the parts to be welded by friction generated in a controlled manner by the oscillation of the parts relative to each other. In addition to the oscillation, the parts are forced together under a controlled load applied perpendicular to the surfaces in contact, referred to herein as the “forge load.” Referring to prior art FIG. 8, in the process, the base part 800 is typically held stationary while part 802 to be welded to the base part is oscillated along oscillation axis 804. With the forge load 806 applied, the oscillation motion causes the parts to heat at the rubbing surfaces 808 to a welding temperature below that of the melting point of the material being welded. The localized heating causes the material to reach a predetermined temperature where the material assumes a “plastic state.” While the adjacent materials are in their plastic state, the oscillation motion is stopped and the forge loading force is increased in a forging movement to force the two parts together. Once together, the forge load is held until the part cools, and eventually reduced to zero, completing the weld cycle.
Welds produced by linear friction welding have been shown to be structurally sound and of high quality. Materials such as Titanium that cannot be easily welded by conventional means can be successfully welded using this process. For this reason, parts welded in this manner are particularly desirable in applications where a high degree of structural integrity combined with minimum weight is required, such as in aviation.
Linear friction welding machines and processes are in development that can create Near Net Shape (NNS) Structures that can be machined to produce finished parts. This method of assembling a structure close to a finished part reduces the amount of material and machining time required to produce the final part, thereby greatly reducing part production costs. Conventional linear friction welding machines capable of creating near net shape structures presently utilize a forge load along a single forge axis to accomplish the weld, which is suitable when welding simple, discrete, two plate perpendicular welded structures where load control at the weld interface can be accurately controlled.
When sequential plate part welding or welding at more than one plane of contact is desired, linear friction welding processes utilizing a single forge axis to accomplish the weld present substantial disadvantages. Referring to prior art FIG. 9, part 902 is shown being welded to base part 900 at both base plate weld 904 and angled weld interface 906, which are welded simultaneously. Heat is generated through controlled friction that occurs along oscillation plane 908. Current processes include a forge load applied along a single forge axis 910, which may be positioned perpendicular relative to one of the weld interfaces 904 and 906, or at a predetermined angle relative to the weld interfaces in the plane of the forge axis 910. Since the forge load control is only in one axis, the forge load required to make the two plane weld is a compromise between producing a resultant forge load adequate to weld the angled weld interface 906, and sufficient to make the base plate weld 904.
In this regard, what is desired when making a simultaneous two-plane weld is an apparatus and method that provides an additional forge axis for improving welding performance and extending the welding capabilities of a linear friction welding machine. By providing a second forge axis, the need for angle contact between plates is eliminated and the precise control of the forge load in the second axis is achieved. Further, by adding a second forge axis along which an additional forge load is applied acting at an angle relative to the first forge axis, an order of magnitude of control is added to the linear friction welding process to improve welding performance.